Node texturing in blender 2.8
to add the color to you texture, you need to combine the saturation and hue of the color texture, with the value of the grayscale. To do that you need a separate HSV and a combine HSV node as below.



For the color the simpler is to just take one color from the texture with the color picker. However if you need the color variation, you can use a mapping node with a small scale factor and change the x and y position. Technically the result will not be perfect tho.